A MEMS device is a microdevice that integrates mechanical and electrical elements on a common substrate using microfabrication technology. The electrical elements are formed using known integrated circuit fabrication technology. The mechanical elements are fabricated using lithographic processes that micromachine a substrate to selectively etch away portions of the substrate. Additional layers are often added to the substrate and then micromachined until the MEMS device is in a desired configuration. MEMS devices include actuators, sensors, switches, accelerometers and modulators.
A typical MEMS device relies on the mechanical oscillation of a suspended micron-sized beam. The beam is electrostatically deflected by energizing at least one actuation electrode. During operation of the MEMS device, the beam engages one or more electrical contacts to establish an electrical connection between isolated electrical elements.
The maximum frequency at which the beam can oscillate determines the highest possible speed of the MEMS device. Therefore, MEMS devices are vacuum packaged to minimize any air-damping that might reduce the beam's maximum oscillation frequency. Vacuum packaging also minimizes the adsorption of contaminants by the beam that might adversely effect the oscillating frequency of the beam.
MEMS devices are also packaged in other types of hermetic environments, such as moisture-free environments. Packaging MEMS devices in moisture-free environments enhances contact reliability by minimizing contact corrosion.
Vacuum and other hermetic MEMS packaging is expensive because it typically requires complicated alignment and bonding procedures that are difficult to apply to MEMS packaging. Once the MEMS devices are vacuum packaged, they are usually mounted onto a substrate with other electronic components as part of an integrated circuit. Mounting the MEMS devices separately from the other components that make up the integrated circuit places the MEMS devices a relatively long way from the other components. When there are large distances between components that make up an integrated circuit, the integrated circuit suffers from power dissipation and parasitic effects that are larger than necessary.